Platypus diving ability
In captivity, a platypus has been observed to remain
underwater for up to 14 minutes while resting quietly under a log. When searching
actively for food, a platypus will usually remain submerged for less than
a minute before returning to the surface to breathe.
Like most diving mammals, the platypus has blood that
is very rich in oxygen-carrying haemoglobin and red cells. The platypus
can also reduce its need for oxygen when diving by lowering its heart rate
dramatically, from more than two hundred beats per minute to less than ten
beats per minute.
Platypus fur
Platypus fur is extremely fine and even denser than
that of polar bears and river otters, with 600-900 hairs covering each square
millimetre of skin! Platypus fur also has two layers - a woolly undercoat
and longer, shiny guard hairs - which work together to trap a layer of air
next to the skin, keeping most of the animal's body dry even when diving.
For the platypus to stay warm while in the water, its
fur must remain completely clean and waterproof, and not be fouled by oil
or other pollutants.
Body temperature
A healthy platypus normally maintains its body temperature
at close to 32 oC, about 5 oC less than that of humans. This reduces the rate at which
a platypus loses heat to the water, helping to ensure that the animals don't
become chilled even when swimming all night in near-freezing conditions.
The combination of a naturally low body temperature
and thick fur coat also means that the platypus overheats rapidly if exposed
to warm conditions on land.
Electroreception system
The platypus hunts underwater and, predominantly, at
night. In such conditions, hearing and eye-sight are of little use in detecting
prey. Accordingly, the platypus closes both its eyes and ears (which are
located in a groove behind the eyes) and relies on its "sixth sense" - an
electro-receptor system, located in the bill which helps it detect the small
flickers of electricity produced by the aquatic creatures that it feeds
on. The bill also contains various pressure sensors which, together with
the electro-receptors, probably assist navigation while submerged.
The platypus was once commonly known as a "duckbill".
In fact, its bill is rubbery and flexible, not hard like that of a duck.
Although the bill is quite tough, to enable the platypus to search for food
amongst rocks and gravel, it is covered with skin. Sometimes platypus are
found with scars on their bill, suggesting that they have cut themselves
on sharp objects in the water, such as broken glass and wire, or have been
snagged on fishing hooks.
Swimming
The platypus swims using only its front limbs for propulsion.
The front feet are equipped with large webs of skin that serve as highly
effective paddles. The webs are folded under the foot when the platypus
is out of the water, making it easier for the animal to walk and use its
strong claws for digging burrows. Unfortunately, these highly specialised
front feet are not adept at removing objects that become caught around the
head or body. As a result, platypus can die after becoming ensnared in litter
such as loops of nylon fishing line or plastic six-pack holders.
The hind legs of the platypus help to steer and stabilise
the animal when it is swimming. The back feet end in a series of sharp,
curved claws that are used like a comb to keep the animal's fur tidy and
waterproof.
Both the front and back legs extend out horizontally
from the body, providing a powerful swimming and digging action. However,
it also forces the platypus to shuffle like a lizard when walking on land
or crossing shallow areas of water, making them vulnerable to predators such
as foxes and dogs.
The tail
Some early reports suggested that the platypus slapped
the water with its tail to make warning sounds, similar in behaviour to
beavers. In fact, there is no evidence for this, although when startled
platypus will sometimes make a "splash-dive" - a rapid dive in which they
seem to use the tail to thrust themselves downwards quickly. This can produce
quite a loud noise, and perhaps this was the origin of the tail-slapping
myth.
The main function of the tail is to store up to 50%
of the animal's body fat, providing an energy reserve if food is scarce.
Researchers rate the general physical condition of a platypus on a five-point
scale by applying a "squeeze test" to the tail in order to assess the amount
of fat stored there.
A female platypus can also use her tail to collect leaves
to make a nest in the breeding chamber. She then uses her curled up tail
to hold eggs against her stomach during incubation.
The platypus tail is broad and paddle-like, quite unlike
the tail of the Australian water-rat (the animal most likely to be confused
with a platypus by observers) which is thin and also has a distinctive white
tip.
Unlike the soft fur on the body of a platypus, the hair
on the upper side of the tail is quite hard and bristle-like, reflecting
the fact that the tail is used to push loose earth out of the way when a
platypus is digging a burrow.
